Messages in this thread Patch in this message |  | | | Date | Mon, 10 Nov 2008 15:39:30 +0100 | | From | Oleg Nesterov <> | | Subject | [PATCH] for account_group_exec_runtime(), make sure ->signal can't be freed under rq->lock |
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The patch is ugly, but I don't see the better fix for now. Needs the review from Peter/Ingo.
Unlike other similar routines, account_group_exec_runtime() could be called "implicitly" from within scheduler after exit_notify(). This means we can race with the parent doing release_task(), we can't just check ->signal != NULL.
Change __exit_signal() to do spin_unlock_wait(&task_rq(tsk)->lock) before __cleanup_signal() to make sure ->signal can't be freed under task_rq(tsk)->lock. Note that task_rq_unlock_wait() doesn't care about the case when tsk changes cpu/rq under us, this should be OK.
Thanks to Ingo who nacked my previous buggy patch.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> Reported-by: Doug Chapman <doug.chapman@hp.com>
--- K-28/include/linux/sched.h~SIG_RQ_LOCK 2008-11-06 19:12:44.000000000 +0100 +++ K-28/include/linux/sched.h 2008-11-10 13:13:07.000000000 +0100 @@ -247,6 +247,7 @@ extern void init_idle(struct task_struct extern void init_idle_bootup_task(struct task_struct *idle); extern int runqueue_is_locked(void); +extern void task_rq_unlock_wait(struct task_struct *p); extern cpumask_t nohz_cpu_mask; #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ) --- K-28/kernel/sched.c~SIG_RQ_LOCK 2008-11-06 19:12:44.000000000 +0100 +++ K-28/kernel/sched.c 2008-11-10 13:05:09.000000000 +0100 @@ -969,6 +969,14 @@ static struct rq *task_rq_lock(struct ta } } +void task_rq_unlock_wait(struct task_struct *p) +{ + struct rq *rq = task_rq(p); + + smp_mb(); + spin_unlock_wait(&rq->lock); +} + static void __task_rq_unlock(struct rq *rq) __releases(rq->lock) { --- K-28/kernel/exit.c~SIG_RQ_LOCK 2008-11-06 19:11:02.000000000 +0100 +++ K-28/kernel/exit.c 2008-11-10 15:07:22.000000000 +0100 @@ -141,6 +141,11 @@ static void __exit_signal(struct task_st if (sig) { flush_sigqueue(&sig->shared_pending); taskstats_tgid_free(sig); + /* + * Make sure ->signal can't go away under rq->lock, + * see account_group_exec_runtime(). + */ + task_rq_unlock_wait(tsk); __cleanup_signal(sig); } }
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